In the design of any machine, and particularly a machine having rotating parts, there is an anticipated finite life expectancy for the machine in terms of the number of duty cycles through which the machine may operate. That is because rotating components in the machine are subject to varying mechanical and thermal loadings, oftentimes severe. For example, in the case of turbines, the design of the machine includes a calculation of its operating life. A complete duty cycle typically includes operation between on and off cycles for the machine. For example, a complete duty cycle for design purposes assumes the machine is initially started and takes a certain time to attain full speed, a load is applied, the machine is maintained under full or partial load, the load is removed, and the machine coasts down to zero speed and stops. A cycle of this type is fairly representative of actual use of a machine, such as a turbine, in the field.
The actual duty cycle of a machine, however, differs from the assumed or calculated cycle. That is, customers may operate their machinery in modes considerably different than assumed during the design of the machine. Consequently, the assumed or design cycle may be too liberal, involving risk of component failure, or too conservative, such as to understate the anticipated life of the machine. Consequently, if the actual duty cycle can be monitored and its actual severity ascertained, its effect on the remaining cyclic life of the machine can be established and, hence, the calculated useful life of the machine can be more accurately predicted in a given installation.